Penile plethysmography (PPG) or phallometry is a measurement of blood flow to the penis, typically used as a proxy for measurement of sexual arousal. The most commonly reported methods of conducting penile plethysmography involves the measurement of the circumference of the penis with a mercury-in-rubber or electromechanical strain gauge, or the volume of the penis with an airtight cylinder and inflatable cuff at the base of the penis. Corpora cavernosa nerve penile plethysmographs measure changes in response to inter-operative electric stimulation during surgery. The volumetric procedure was invented by Kurt Freund and is considered to be particularly sensitive at low arousal levels. The easier to use circumferential measures are more widely used, however, and more common in studies using erotic film stimuli. A corresponding device in women is the vaginal photoplethysmograph.Prause, Nicole, and Erick Janssen. "Blood flow: Vaginal photoplethysmography." Women's sexual function and dysfunction: Study, diagnosis, and treatment (2006): 359-367.
For sexual offenders it is typically used to determine the level of sexual arousal as the subject is exposed to sexually suggestive content, such as pictures, movies or audio, although some have argued that phallometry is not always appropriate for the evaluation of sexual preferences or treatment effects. A 1998 large-scale meta-analytic review of the scientific reports demonstrated that phallometric response to stimuli depicting children, though only having a .32 correlation with future sex offending (accounting for approximately 10% of the variance), had the highest accuracy among methods of identifying which sexual offenders will go on to commit new sexual crimes. (None of the methods were strong predictors with most accounting for far less than 10% of the variance).
In prostatectomy nerve-sparing surgery, the surgeon applies a mild electrical stimulation near the cavernous nerves of penis to verify their locations and avoid operative trauma. Damage to these difficult-to-see nerves can cause erectile dysfunction outcomes. At the surgery's conclusion, the electrical stimulation penile plethysmograph result is a prognosis which helps to manage the erectile function outcomes earlier than the many months required for recovery.
Types
There are two types of penile plethysmograph: Volumetric air chamber When this is placed over the subject's penis, as tumescence increases, the air displaced is measured. Circumferential transducer This uses a mercury-in-rubber or indium/gallium-in-rubber ring or electromechanical strain gauge and is placed around the shaft of the subject's penis to measure changes in circumference.
The circumferential type is more common, but the volumetric method is believed to be more accurate at low arousal levels.
Significant suppliers of PPG machines include Behavioral Technology Inc. and Medical Monitoring Systems. The device is known to be used in Brazil, Britain, Canada, China, Czech Republic, Hong Kong, New Zealand, Norway, Slovak Republic, Spain, and the United States.
The surgical machine is supplied as CaverMap by Blue Torch Medical Technology, Inc.
A roughly equivalent procedure for women, vaginal photoplethysmography, measures blood through the walls of the vagina, which researchers claim increases during sexual arousal.
Methodology Exact procedures can vary, but in one study a seventeen-year-old male sex offender was, at the start of each daily session, privately fitted with a Parks Medical Electronics mercury strain gauge attached to his penis and worn under trousers and underwear. The device had previously been calibrated with measurements from his penis in its flaccid state and at full erection as achieved through masturbation. This device was connected to a microprocessor, a battery pack, and a strain gauge amplifier, all of which were kept discreetly in a fanny pack. He was then driven daily to a college campus for multiple sessions to assess his sexual attraction to women and men, who were about 30–100 feet away from him. While remaining in a parked car, he was instructed to focus on either a specific woman or a specific man in the setting, imagine himself having sex with them, and allow himself to become sexually aroused if he was so inclined. The device then measured the percentage of full erection that he achieved. This was repeated over a period of 24 days, with the results showing a significantly greater level of attraction to women, especially when research staff were discreetly absent.
History The original volumetric was developed during the 1950s by Kurt Freund in then-Czechoslovakia. Freund later wrote, "In the early fifties homosexual interaction was still an indictable offense in Czechoslovakia. I was of course opposed to this measure, but I still thought, as did my colleagues at the psychiatric university hospital in Prague where I was working, that homosexuality was an experientially acquired neurosis". He then developed phallometry to replace psychoanalytic methods of assessment because "[P]sychoanalysis had turned out to be a failure, virtually unusable as an instrument for individual diagnosis or research....When phallometry began to look promising as a test of erotic sex and age preferences, we started using it mainly as a test of pedophilia, that is determining who has an erotic preference for children over adults".
In post-World War II Czechoslovakia, Freund was assigned by the communist government the task of identifying among military conscripts men who were falsely declaring themselves to be gay to avoid the draft.Wilson, R. J., & Mathon, H. F. (2006, fall). Remembering Kurt Freund (1914-1996). ATSA Forum. Beaverton, OR: Association for the Treatment of Sexual Abusers. "Freund (1957) developed the first device, which measured penile volume changes... to distinguish heterosexual and homosexual males for the Czechoslovak army."W O'Donohue, E Letourneau. The psychometric properties of the penile tumescence assessment of child molesters. Journal of Psychopathology and Behavioral Assessment, 1992 When he escaped Europe for Canada, Freund was able to pursue his research using phallometry for the assessment of sexual offenders. At that time, attempts to develop methods of changing homosexual men into heterosexual men were being made by many sexologists, including John Bancroft, Albert Ellis, and William Masters of the Masters and Johnson Institute. Because phallometry showed that such methods were failures, Freund was among the first sexologists to declare that such attempts were unethical. Based primarily on Freund's studies, decriminalization of homosexuality took place in Czechoslovakia in 1961. (See also LGBT rights in the Czech Republic.)
Reliability and validity In 1994, the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition) of the American Psychiatric Association stated that penile plethysmography has been used in research settings to assess various paraphilias by measuring an individual's sexual arousal in response to visual and auditory stimuli. The reliability and validity of this procedure in clinical assessment have not been well established, and clinical experience suggests that subjects can simulate response by manipulating mental images."DSM-IV, p. 524. In contrast, a 2017 recent meta-analysis provides support for the validity of phallometric testing as a measure of sexual interests in children across 37 samples and 6,785 individuals.
In 1998, Hanson and Bussière published a comprehensive meta-analysis of 61 scientific reports on the prediction of sexual offenses spanning more than 40,000 individual cases. They ascertained that of all the methods attempted and reported, penile phethysmographic responses to imagery depicting children was the single most accurate predictor of sexual re-offense across 7 studies reporting data from phallometric testing. Another meta-analysis in 2005 of 13 studies and 2,180 individual cases repeated the finding that phallometric responses to children was a strong predictor of sexual re-offense.
A 2017 meta-analysis that included 16 samples and 2,709 sexual offenders replicated and extended the previous findings that phallometric responding to children is a predictor of sexual re-offence. This meta-analysis extended previous meta-analytic research by showing phallometric responding to both male and female pedophilic and hebephilic stimuli predict sexual re-offence. Further, this meta-analysis showed that phallometric testing predicts sexual re-offence in distinct subgroups of sexual offenders against children.
Critique of methodological problems There are criticisms of the methodology used to determine the reliability and specificity of penile plethysmography. One such criticism is that while penile plethysmography is said to be important for being more objective than a test subject's subjective reports on sexual arousal, the argument for penile plethysmography being a more reliable gauge of sexual arousal than vaginal plethysmography is still that there is a higher correspondence on average between what the test subjects report and what the instruments observe in male subjects than in female subjects. There is a criticism of this discrepancy for lacking consistency in the standards of whether or not subjective reports are useful. There is also criticism regarding the possibility of sampling bias being greater in male subjects of penile plethysmography than in female subjects of vaginal plethysmography, males being generally more aware of their physical sexual responses than females in most cultures may cause the male volunteers to be almost exclusively individuals who have category specific erections due to those with nonspecific erections fearing erection in taboo contexts and therefore not signing up for the studies. This effect may explain apparent male specificity as a result of methodological bias. The difference between tests of volunteers and tests of convicted or suspected sex offenders in penile plethysmography results may be caused by the sex offender group often effectively lacking the choice not to volunteer, without difference in erection patterns from the average population. One criticism of reoffending studies is that cultural attitudes that assume that men are sexually attracted to what they phallometrically respond to may cause men with no actual sexual interest in children to identify as pedophiles due to knowing that they phallometrically respond to them, making them more likely to be convicted again.Science and Pseudoscience in Clinical Psychology, Scott O. Lilienfeld, Steven Jay Lynn, Jeffrey M. Lohr 2015At the Fringes of Science, 1998, Michael W. Friedlander
Utility
Erectile dysfunction The penile plethysmograph has value in screening organic versus psychogenic erectile dysfunction in urological polysomnography centres. Lack of sexual response during REM sleep may indicate that further evaluation by a urologist is required.
When applied during nerve-sparing surgery, electrical stimulation penile plethysmograph is an erectile dysfunction prognostic. The patient is provided with objective information on his specific outcome which aids in planning for further erectile function therapies.
Pedophilia, hebephilia, pedohebephilia, and ephebophilia